The present invention relates to improvements in flexible extruded plastic fasteners having interlocking complementary profiles constructed and arranged to be pressed into interlocked relation.
Flexible extruded plastic profile fasteners are normally provided with a rib element which is arranged to be pressed into interlocking relationship into a groove element. The fasteners are commonly used on bags and pouches but also find utility in attaching two mating parts, such as attaching a sheet of plastic to another sheet of plastic. While structures frequently adopted permit pressing the complementary profiles together to interlock them and permit forcible separation by pulling the profiles apart, profiles have been found to be quite expedient as a means for a simplified permanent fastener. Such fasteners may be used in a structure such as at the top of a container where the container is to be filled and thereafter permenently sealed. The container will be openable by other means, such as tearing open the top, or on occasion by separating the profiles by a special tool. In each case means are provided for retaining the interlocked profiles substantially against separation. U.S. Pat. No. 3,808,649 relates to a non-reopenable construction which requires a tool for interlocking the profiles. U.S. Pat. No. 4,290,467 discloses an interlocked profile construction wherein the profiles are difficult to open from the outside of the bag because of the closely trimmed flanges at the outside of the zipper. Other means may be employed to essentially permanently interlock the profiles, such as utilization of an adhesive or heat welding the profiles together. The present invention pertains principally to arrangements for an improved structure wherein the profiles are designed to be essentially permanently interlocked.
In connection with the use and handling of profiles which have a permanent interlocking feature, it is desirable that the profiles can be handled and stored without becoming interlocked prior to usage. For example, if the profiles are to form a permanent closure for the top of a bag, it is necessary that the bag can be handled and stored such as by stacking in a container without the profiles becoming closed because they cannot be simply reopened. If the profiles inadvertently become interlocked through the application of small pressure such as encountered in stacking a number of bags or in handling them, the bags become unusable because they cannot be filled without some special arrangement for opening them, and this become impractical for bags for commercial use.
It is accordingly an object of the present invention to provide a method and structure for interlocking profiles wherein the closure profiles can sustain the forces of normal handling and storage without accidentally becoming interlocked.
A further object of the invention is to provide a complementary profile structure having an arrangement wherein they can be forcibly pressed to permanent interlocking relationship, but normal processing, handling and storage forces do not cause interlocking of the profiles.
In the provision of interlocking profiles, it is economically expedient to manufacture the profiles that do not use more plastic than necessary. The size and design of the profile is governed by the minimum amount of plastic needed to provide a strength which will prevent accidental tearing or reopening of the profiles through normal handling and usage of the filled bag. To provide more plastic or heavier parts than are needed for the essential nonopening function increases the expense unnecessarily and obtains a more weighty and bulky structure than needed. With reliable designs which obtain permanently interlockable rib and groove profiles, the profiles can be made of a relatively small size and still provide adequate strength for their purpose. A difficulty with such a small size is that it is essential that the rib and groove profiles be kept in alignment so that they will interlock when pressed together. This alignment is hard to maintain with very small profiles when the fastener may sustain considerable handling prior to use and during filling.
It is accordingly an object of the present invention to provide an improved structure which maintains the profiles in alignment until they are permanently interlocked and insures that the rib element will be in the proper location relative to the groove element to readily interlock when a sufficient closing pressure is applied.
In accordance with features of the invention, the structure of the rib and groove element is such that the rib at all times will remain positioned opposite the groove element at one location so that when the application of a progressive pressure is applied to join the rib and groove element, they will readily and immediately join. With the use of automatic equipment, this reliability of joining becomes essential because if the two closure elements get out of alignment and a closing pressure is applied, they will not join and a reject will occur. That is, the rib and groove will not interlock and substantial difficulty is encountered in trying to get them back into alignment or as an alternative, the bag and its contents will have to be discarded. It is also important that interlocking reliably occur because bags cannot be sent out into the marketplace which are not properly closed, and this is particularly essential with rib and groove elements where they are permanently joined once they are pressed to closed relationship.